Earthmoving equipment, such as bull dozers, may include joystick handles to control the direction and speed of the machine. For example, moving the joystick to the left or right may control the direction of the machine, while moving the joystick fore or aft may control the velocity. Operators desire a way to hold the joystick in a desired position for an extended period of time, for example, when dozing in a specific direction. When moving in the same direction for an extended period of time operators do not want to have to concentrate on holding the joystick steady. Therefore, systems have been developed that enable the operator to lock the joystick in a particular position while moving. An electromagnetic lock may be used to perform the locking function. In general, the electromagnetic lock includes two coils which, when energized, create a magnetic field locking the joystick in place. When the operator turns the electromagnetic lock off they desire the joystick to return to the center position. Having the joystick return to center position is important when the operator applies the brakes, or disengages the cruise control of the machine. When the electromagnetic lock is disengaged the operator needs to manually control the direction of the machine. However, current electromagnetic locks have a residual magnetism when they are turned off. The residual magnetism continues to create an electromagnetic force even though the lock has been disengaged. The residual magnetism makes it difficult for an operator to restore manual control of the machine because the residual force holds the joystick off neutral.
In addition, operators need multiple levels of forces applied to the joystick depending on what operation the machine is performing. For example, if the operator is moving to another location they may want a large level of force applied to the joystick because the machine does not need to make velocity changes; and, therefore, a force can be applied which will hold the joystick in place despite the vibration the joystick experiences. On the other hand, if the operator is moving dirt from one location to another during dozing, the operator may want an intermediate level of force applied to the joystick so that the operator may make small velocity corrections of the machine without having to disengage the cruise control, which disengages the locking force. Therefore, multiple levels of force are desirable, and the force applied needs to be selected by the operator.
The present invention is directed to overcoming one or more of the problems set forth above.